a) Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device.
b) Description of the Related Art
During a manufacturing process of a semiconductor device, a diffusion barrier is frequently formed on an interior wall of a hole such as a contact hole or via hole, in order to prevent a metal such as copper used for a metal line from diffusing into underlying silicon and/or an adjacent oxide. The diffusion barrier must have conductivity, and typical examples thereof are titanium nitride (TiN), tungsten nitride (WN), and tantalum nitride (TaN).
Recently, copper has frequently been used for metal lines in semiconductor devices instead of aluminum, in order to improve device characteristics, such as operating speed or resistance. This copper has merits such as low resistivity and high melting point, but it also has drawbacks as described below.
For example, copper has no fine protective layer such as Al2O3, it shows poor adhesion to silicon dioxide (SiO2), and it is difficult to dry etch. In addition, copper has a diffusion coefficient about 106 times higher than that of aluminum in silicon, and the diffused copper forms a deep energy level between band gaps. In addition, copper also has a high diffusion coefficient in SiO2, and accordingly, an insulating property between the copper lines may deteriorate. As a result, the high diffusion coefficient of Cu in silicon or SiO2 may substantially deteriorate reliability of a semiconductor device.
Therefore, in order to ensure sufficient reliability during a copper line process, there is a need for a diffusion barrier that can prevent copper from rapidly diffusing into silicon or SiO2.
As above-described, the diffusion barrier plays an important role in interconnections. Therefore, it is important to develop a technique that is capable of forming a fine diffusion barrier. TaN, for example, is thermodynamically stable with copper. Accordingly, many methods have been developed to use a TaN thin film as a fine diffusion barrier during the copper line manufacturing process.
TaN thin films generally have high thermal stability, excellent adhesion to the oxide layer, and a desirable diffusion barrier characteristic. Accordingly, TaN thin films are widely used as a diffusion barrier. Generally, the TaN thin film is formed of a TaN/Ta bi-layer with a thickness of 100 nm or more by a physical vapor deposition (PVD) method.
As semiconductor devices have become smaller, Cu lines with a width of 65 nm or less are desired. Accordingly, the TaN thin film must have a thickness of less than 5 nm. However, according to the PVD method, the TaN thin film generally cannot realize sufficiently uniform step coverage at such thicknesses. In order to overcome this non-uniform deposition and to acquire excellent step coverage and a desirable diffusion barrier characteristic, an atomic layer deposition (ALD) method has been developed.
The ALD method employs a precursor (for example, a metal-organic precursor and a halogen compound such as TaCl5) to form or deposit a TaN thin film. However, when the TaN thin film is deposited by the ALD method employing the metal-organic precursor, the TaN thin film may include a substantial amount of carbon. In this case, a low film density and high resistivity result, such that the copper lines may not have desired electric characteristics.
Therefore, research has been undertaken to employ the halogen compound such as TaCl5 as a precursor for the diffusion barrier. However, in this case, impurities such as Cl may cause corrosion to the copper lines such that reliability of the semiconductor device may deteriorate.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form information or prior art that may be known in this or any other country to a person of ordinary skill in the art.